Vibrational studies of benzene, pyridine, pyridine-N-oxide and their cations

•Pyridine is one of the building blocks of a large number of biologically important molecules.•N–O moiety possesses a unique functionality of acting effectively as a push electron donor and a pull electron acceptor.•Pyridine is used as a precursor to agrochemicals and pharmaceuticals.•Due to removal of electron all the fundamentals are affected in pyridine/pyridine-N-oxide.

IR and Raman spectra of pyridine and pyridine-N-oxide have been recorded and analyzed. The optimized molecular geometries, APT charges and vibrational characteristics for benzene, pyridine, pyridine-N-oxide and their cations have been computed using DFT method. Due to attachment of O atom at N site or removal of electron all the modes are affected in magnitudes. However, significant changes are noticed in their IR intensities, Raman activities and depolarization ratios of the Raman bands in going from pyridine to its N-oxide or in going from neutrals to their cations. It is interesting to note that in going from benzene to benzene cation charge redistribution takes place to reduce the symmetry from D6h to D2h. The calculated frequencies have been correlated with the experimental frequencies for the pyridine and pyridine-N-oxide molecules.

Graphical abstractThe computed IR spectra for the Bz, Bz+, Py, Py+, PyO and PyO+ molecules were carried out using the Gaussian-03 software at the B3LYP/6-311++G** level.Figure optionsDownload full-size imageDownload as PowerPoint slide